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This looks like human error to me, either a clerk's misspelling, or a misreading of poor handwriting. I take it the source of this information is a handwritten record or records.
Donnellan to Donnelly looks like a clerical error. One name must be wrong, I'd suggest the one that didn't survive, though you never know.
As for Lnu, how about some name like Lin, which would in itself be a misspelling of Linn? Or Lunn? Just a guess, but I've seen documents in which a succession of letters with vertical strokes - i ,n, m, u, written by a poor penman, become indistinguishable.
If it's possible try to go back to your original text and consider other interpretations.